The present invention relates to a reception quality measurement method, transmission power control method and devices thereof, and more particularly, a reception quality measurement method, transmission power control method and devices thereof for a mobile station that receives F-DCPH symbols and CPICH symbols from a base station.
A W-CDMA (UMTS) mobile communication system is one kind of radio communication interface that is based upon IMT-2000 (International Mobile Telecommunications-2000), and by using a maximum transmission speed of 384 Kbps, makes access of multimedia such as sound, moving images, data and the like possible. As shown in FIG. 11, this W-CDMA mobile communication system comprises: a core network 1; radio base station control devices (RNC: Radio Network Controllers) 2, 3; multiplexing/separation devices 4, 5; radio base stations (Node B) 61 to 65; and a mobile station (UE: User Equipment) 7. The core network 1 is a network for performing routing in the mobile communication system; for example, the core network can be an ATM exchange network, packet exchange network, router network, etc. The core network 1 is also connected to other public networks (PSTN), making it possible for a mobile station 7 to perform communication between itself and a fixed telephone or the like.
The radio base station control devices (RNC) 2, 3 are located as host devices to the radio base stations 61 to 65, and comprise functions for controlling these radio base stations 61 to 65. The radio base station control devices 2, 3 also comprise a handover control function so that during handover, signals from one mobile station 7 are received by way of a plurality of subordinate radio base stations, and the data is selected from the signal having the best quality and transmitted to the core network 1.
The multiplexing/separation devices 4, 5 are located between the RNC and radio base stations, and they perform control for separating signals that are received from the RNC 2, 3 and destined for each of the radio base stations, and together with outputting those signals to the radio base stations, multiplex signals from the radio base stations and transfer them to each RNC.
The radio base stations 61 to 65 perform radio communication with the mobile station 7, and are such that RNC 2 manages the radio resources of the base stations 61 to 63, and RNC 3 manages the radio resources of the base stations 64, 65. The mobile station 7 establishes a radio communication between itself and a radio base station 6i when it is within the radio communication area of the radio base station 6i, and performs communication between itself and another communication terminal by way of the core network 1.
HSDPA
A typical W-CDMA mobile communication system has been explained above, however, the HSDPA (High Speed Downlink Packet Access) method is further employed as a technique for making high-speed transmission in the down link direction possible. HSDPA uses an adaptive encoding modulation method (AMC: Adaptive Modulation and Coding); for example, this method is characterized by adaptively switching between a QPSK modulation method (QPSK modulation scheme) and a 16-value QAM method (16 QAM scheme) according to the state of radio communication between the radio base station and mobile station. The HSDPA method also uses a H-ARQ (Hybrid Automatic Repeat request) method. In the H-ARQ method, when the mobile station detects an error in data received from the radio base station, the mobile stations sends a request (sends a NACK signal) to the radio base station to resend the data. The radio base station that receives this resend request resends the data, so the mobile station that has already received the data uses both this data and the resent data that it receives to perform error correction decoding.
As shown in FIG. 12, the main radio channels that are used in HSDPA are as follows:
(1) HS-SCCH (High Speed-Shared Control Channel,
(2) HS-PDSCH (High Speed-Physical Downlink Shared Channel),
(3) HS-DPCCH (High Speed-Dedicated Physical Control Channel),
HS-SCCH and HS-PDSCH are both shared channels in the downlink direction (downlink in the direction from the radio base stations to the mobile station), where HS-SCCH is a control channel for sending to the mobile stations various kinds of parameters related to the data that is sent by HS-PDSCH. The various kinds of parameters could be destination information that indicates which mobile station data is to be sent to, transmission bit rate information, modulation method information that indicates which modulation method is used in sending data by HS-PDSCH, allotment number (code number) for spreading codes, a pattern for rate matching that is performed for the transmission data, etc.
On the other hand, HS-DPCCH is an individual control channel (dedicated control channel) for the uplink direction (uplink in the direction from the mobile station to the radio base station), and is used when the mobile station sends reception results (ACK signal, NACK signal) depending on whether or not there was error in the data received via the HS-PDSCH. That is, it is a channel that is used for sending reception results for data that is received via the HS-PDSCH. When a mobile station fails to receive data (there is a CRC error or the like in the reception data), the mobile station sends a NACK signal, so the radio base station executes resend control.
Transmission Power Control
In W-CDMA mobile communication, by identifying each of channels according to the spreading code that is allotted to each channel, a plurality of channels perform communication by sharing one frequency bandwidth. However, in an actual mobile communication environment, the reception signal receives interference from its own channel and other channels due do the delay wave in multipath fading or a radio signal from another cell, and that interference has an adverse effect on channel separation. Moreover, the amount of interference that the reception signal receives changes over time due to instantaneous fluctuation in the reception power caused by the multipath fading, or change in the number of users communicating at the same time. In a communication environment in which the interference that changes over time generates in this way, it is difficult to stabilize and maintain the quality of the reception signal at the mobile station connected to the base station at a desired level of quality. In order to cope with this kind of change in the number of interfering users or the instantaneous fluctuation in values due to the multipath fading, the receiving side (mobile station) measures the signal to interference power ratio (SIR), and by comparing the measured SIR with a target SIR, transmission power control is performed to bring the SIR of the mobile station close to the target SIR.
FIG. 13 is drawing explaining transmission power control of a mobile station, and shows only one channel. The spreading modulation unit 6a of the base station 6 uses a spreading code that corresponds to a specified channel to spread and modulate transmission data, a power amplifier 6b amplifies the signal obtained by processing such as quadrature modulation and frequency conversion after the spreading modulation, and the amplified signal is sent to the mobile station 7 from the antenna. The inverse spreading unit 7a of the reception unit of the mobile station 7 performs inverse spreading on the reception signal, and the demodulation unit 7b demodulates the reception data. The SIR measurement unit 7c measures the power ratio between the reception signal and interference signal. The comparison unit 7d compares the measured SIR with a target SIR, and when the measured SIR is greater than the target SIR, creates a command to lower the transmission power by the TPC (Transmission Power Control) bit, and when the measured SIR is less than the target SIR, creates a command to raise the transmission power by the TPC bit. The target SIR is the SIR value that is necessary for obtaining 10−3 (error occurrence rate of 1 time per 1000 times), and this value is input to the comparison unit 7d from the target SIR control unit 7e. The spreading modulation unit 7f spreads and modulates the transmission data and TPC bit. After spreading and modulation, the mobile station performs processing such as DA conversion, quadrature modulation, frequency conversion and power amplification, and sends the result to the base station 6 from the antenna. The inverse spreading unit 6c on the base station side performs inverse spreading on the signal received from the mobile station 7, the demodulation unit 6d demodulates the reception data and TPC bit, and controls the transmission power of the power amplifier 1 according to the command indicated by that TPC bit. The transmission power control described above is called inner-loop transmission power control.
FIG. 14 is a drawing showing the configuration of the individual physical channel DPCH (Dedicated Physical Channel) frame in the uplink that is normalized by the 3rd Generation Partnership Project (hereafter, referred to as 3GPP). The dedicated physical channel DPCH comprises a DPDCH channel (Dedicated Physical Data Channel) by which only transmission data is transmitted, and DPCCH channel (Dedicated Physical Control Channel) by which control data such as a pilot and the TPC bit information that was explained in FIG. 13 are multiplexed and transmitted. The data transmitted by the DPDCH channel and DPCCH channel are spread by respective orthogonal code, after which the data is mapped and multiplexed on the real number axis and imaginary number axis. One frame in the uplink is 10 msec, and is configured with 15 slots (slot #0 to slot #14). The DPDCH channel is mapped on the I channel, and the DPCCH channel is mapped on the orthogonal Q channel. Each slot of the DPDCH channel comprises n bits, where n changes according to the symbol speed. Each slot of the DPCCH channel that transmits control data comprises 10 bits, where the symbol speed is fixed at 15 ksps, and transmits a pilot Pilot, transmission power control data TPC, transport format combination indicator TFCI, and feedback information FBI.
Due to changes in the propagation environment due to movement or change in the speed of movement during communication, the SIR that is necessary in order to obtain the desired quality (block error rate: BLER) is not fixed. BLER is the ratio between the total number of transport blocks (TrBk) during a fixed period, and the number of TrBk for which a CRC error occurred. In order to deal with this change, transmission power control further observes the BLER, and when the observed value is worse than the set target BLER, increases the target SIR, and when the observed value is better than the set target BLER, decreases the target SIR. In other words, at the same time as inner-loop transmission power control, the mobile station performs outer-loop transmission power control to control the target SIR in order to obtain the desired quality (block error rate BLER).
In FIG. 13, after the required BLER is specified according to the type of service from the host application, the target SIR control unit 7e inputs a target SIR that corresponds to the required BLER to the comparison unit 7d. At the same time as the inner-loop transmission power control described above, the error-correction decoding unit 7g performs error detection/correction and decoding of the demodulated result from the demodulation unit 7b, and inputs the decoded result to the CRC detection unit 7h. The CRC detection unit 7h separates the decoded data into transport blocks TrBk, and then performs CRC error detection of each transport block TrBk and inputs the error detection results to the target SIR control unit 7e. The target SIR control unit 7e measures the actual BLER based on the error detection result, then compares the measured BLER with the required BLER, and when the reception state is poor and the measured BLER is greater than the required BLER, performs control to increase the target SIR, however when the reception state is good and the measured BLER is less than the required BLER, performs control to decrease the target SIR. By performing this outer-loop transmission power control, it is possible to control the transmission power so that the required BLER can be obtained.
F-DPCH
In a W-CDMA communication system that employs the HSDPA method, the user (mobile station) is able to receive data over a HS-PDSCH, which is a shared channel (see FIG. 12), and at the same time is able to receive data over an individual channel DPCH (Dedicated Physical Channel).
FIG. 15 shows an example of the format of the dedicated physical channel DPCH in the downlink from a base station to a mobile station. One frame comprises 15 slots, slot #0 to slot #14, and each slot is configured so that a first data section Data1, TPC information, TFCI information, second data section Data2 and Pilot information are transmitted by time division multiplexing. The downlink dedicated channel DPCH is comprised of a DPDCH (Dedicated Physical Data Channel) that transmits data, and a DPCCH (Dedicated Physical Control Channel) that transmits control data (TPC information, TFCI information, Pilot).
In a W-CDMA communication system that employs the HSDPA method, in most cases there is no data to be transmitted over the dedicated channel to a user (mobile station) that is receiving data at high speed over the shared channel such as HS-PDSCH. However, even though there is no data to be transmitted over the dedicated channel DPCH, it is necessary for the base station to transmit specified symbols (for example, a TPC symbol) over the dedicated channel DPCH in order to perform the transmission power control described above. That is, the base station must connect to the dedicated channel DPCH at the same time as the shared channel HS-PDSCH, so even though it may not be necessary to transmit data over the dedicated channel DPCH, one spreading code is occupied for sending the TPC symbol, and as a result, when there is a plurality of similar users, a problem will occur in that there will not be enough resources.
A F-DPCH (Factional Dedicated Physical Channel) is a channel that is normalized by 3GPP release 6 (3rd Generation Partnership Project Release 6) in order to solve this problem, wherein it has frame configuration as shown in FIG. 16, and an individual channel transmits only transmission power control information (TPC symbol). The base station assigns one spreading code to F-DPCH, and spreads that F-DPCH by that spreading code, and as showing in FIG. 17 by making the transmission timing (offset) different for each user, performs transmission so that TPC symbols do no overlap between different users. In other words, the base station uses a F-DPCH instead of the dedicated channel DPCH to transmit only a TPC symbol to a user for which there is no data to transmit over the dedicated channel DPCH, and in so doing solves the problem of insufficient resources.
In transmission power control by the dedicated channel DPCH, in order to perform high-precision TPC control, two kinds of control are performed, inner-loop transmission power control that measures SIR and performs control so that the measured SIR will become a target SIR, and outer-loop transmission power control that performs CRC computation and measures the BLER and corrects the target SIR so that the measured BLER becomes the required BLER. However, since data is not transmitted over a F-DPCH, a CRC signal is not added to the data format of the F-DPCH. Therefore, when transmission is performed using F-DPCH instead of DPCH, it is not possible to perform outer-loop transmission power control. In that case, the control method described below is adopted in transmission power control when performing transmission using F-DPCH. In other words, a method is employed in which a correspondence table that shows the correspondence between the target SIR of the TPC symbol received from the base station and the target error rate of the F-DPCH is used, and when the required F-DPCH target error rate is set, the target SIR is found from that table and control is performed so that the measured actual SIR of the TPC symbol coincides with that target SIR.
FIG. 18 is a drawing explaining the transmission timing of a downlink F-DPCH that is transmitted from the base station, and a DPCCH (see FIG. 14) that is transmitted from the mobile station and includes a TPC bit. The F-DPCH is transmitted being delayed a specified offset Toff for each user from a reference timing T0 at which the downlink CPICH (Common Pilot Channel) or P-CCPCH (Primary Common Control Physical Channel) is transmitted. The mobile station receives the TPC bit that is included in the F-DPCH and measures the SIR, then performs transmission power control based on that SIR. After a time of 1024 chips from the transmission timing of the F-DPCH, the mobile station transmits an uplink DPCCH that includes a TPC bit, which is the transmission power control data, to the base station. The timing that this uplink DPCCH is transmitted to the base station is a time that set according to the 3GPP and is a fixed time.
Conventional Mobile Station
FIG. 19 is a drawing showing the construction of a conventional mobile station, and shows the main construction of parts for receiving the TPC bit that is included in the F-DPCH, measuring the SIR, performing transmission power control based on that SIR, setting a TPC bit as transmission power control information, and sending an uplink DPCCH that includes that TPC bit to the base station.
The radio signal that is sent from the base station is received by the antenna and input to the receiver 11. After performing down conversion of the radio signal to a baseband signal, the receiver 11 performs processing such as quadrature modulation, AD conversion, inverse spreading and the like on the obtained baseband signal, and outputs a F-DPCH symbol signal, CPICH symbol signal and reception timing signal (frame synchronization signal, slot synchronization signal). A channel estimation filter 12 used for calculating the RSCP (Received Signal Code Power) calculates the average value of the previous n symbols to the current symbol, for example the average of 10 symbols, of the CPICH symbol signal, then computes the channel estimation value from that average value and outputs it at the symbol cycle. One slot of the CPICH comprises 10 symbols, so these 10 symbols are equivalent to the portion of one slot. An RSCP measurement processing unit 13 performs channel compensation on the F-DPCH symbol signal (TPC symbol) based on the channel estimation value input from channel estimation filter 12, then measures the reception power of that TPC symbol and inputs the result to a SIR measurement processing unit 14 as the RSCP.
A channel estimation filter 15 used for calculating the ISCP (Interference on Signal Code Power) calculates the average value of the symbols previous to the current symbol of the CPICH symbol signal, then computes the channel estimation value from that average value and outputs the result at the symbol cycle. An ISCP measurement processing unit 16 calculates the power of the interference signal using a CPICH symbol that was received at the same reception timing as the TPC symbol of the F-DPCH, a known CPICH symbol, and the channel estimation value input from the channel estimation filter 15, and inputs the result to the SIR measurement processing unit 14 as the ISCP. The SIR measurement processing unit 14 uses the input RSCP and ISCP to calculate and output the SIR according to the equation below.SIR=RSCP/ISCP
After the target error rate is set by the UTRAN (UMTS Terrestrial Radio Access Network) 18, a target SIR control unit 17 make a reference to a target error rate/target SIR conversion table 19 to find a target SIR that corresponds to the target error rate, and inputs the result to a TPC command generation unit 20. FIG. 20 shows an example of a target TPC error rate/target SIR conversion table, and FIG. 21 is a graph showing the characteristics of the TPC error rate versus the target SIR, where A is the characteristics in a normal environment.
The TPC command generation unit 20 sets a TPC command (Up or Down) from the measured SIR result and the target SIR, and inputs that TPC command to a DPCCH processing unit (Pilot/TFCI/FBI/TPC scheduling unit) 21.
At the same time as the above processing, a downlink reception timing monitoring unit 22 monitors the downlink timing based on the reception timing signal (frame synchronization signal, slot synchronization signal), and an uplink transmission timing management unit 23 inputs a transmission timing signal to the DPCCH processing unit 21. The DPCCH processing unit 21 performs time division multiplexing of the uplink DPCCH Pilot, TFCI, FBI and TPC, and outputs a DPCCH symbol in synchronization with the transmission timing signal. A DPCCH encoding unit 24 encodes the input DPCCH symbol, a modulation unit 25 performs modulation of the DPCHH and other uplink channels, and a transmitter 26 converts the modulated signal to a radio signal and transmits it toward the base station.
FIG. 22 is a drawing showing a time chart image in symbol units of the calculation process of ISCP, RSCP and SIR in the F-DPCH. When performing demodulation of the F-DPCH by the mobile station, in order to demodulate the TPC symbol STPCn of slot #n, the channel estimation filter 12 for calculating the RSCP performs the channel estimation filtering process using the reception wave of slot #n−1 of the CPICH (step 101). After performing channel compensation of the F-DPCH symbol signal (TPC symbol) based on the channel estimation value, the RSCP measurement processing unit 13 measures the reception power RSCP of that TPC symbol and inputs it to the SIR measurement processing unit 14 (step 102).
The channel estimation filter 15 for calculating the ISCP also performs the channel estimation filtering process using the reception wave of slot #n−1 of the CPICH (step 103). The ISCP measurement processing unit 16 calculates the reception power ISCP of the interference signal using a CPICH symbol that is received at the same reception timing as the TPC symbol of the F-DPCH, a known CPICH symbol and the channel estimation value that was obtained in step 103, and inputs it to the SIR measurement unit 14 (step 104). The SIR measurement processing unit 14 uses the input RSCP and ISCP to calculate and output the SIR (step 105).
By the process described above, the mobile station measures the SIR, then based on the size of the measured SIR and a target SIR, decides the TPC bit, and maps that TPC bit on the uplink DPCCH that is sent 1024 chips after receiving the F-DPCH, and transmits it to the base station. When doing this, the mobile station performs channel estimation using the reception wave of slot #n−1 of the CPICH, and measures the SIR of the TPC symbol of the F-DPCH of slot #n.
The channel estimation value that was measured using the reception wave of slot #n−1 of the CPICH indicates a value at the center time (past time) of that slot #n−1, and is not the channel estimation value at the reception time of the F-DPCH symbol of slot #n. Therefore, if the channel estimation result varies in a short period of time in a fading environment or multipath environment, there generates an environment where the past channel estimation value and current channel estimation value differ, and as a result a phenomenon occurs in which there is deterioration of the ISCP value in regard to the accuracy. The interference power is a physical quantity that is not affected by the fading environment or multipath environment of a mobile device, so in a fading environment or multipath environment, that precision of the ISCP deteriorates. Therefore, the SIR measurement precision of the F-DPCH deteriorates, and it becomes impossible to perform transmission power control with high enough precision to be able to obtain the target error rate as a target.
FIG. 20 is one example of a table for converting the Target TPC Command Error Rate (target error rate) to the SIR of the F-DPCH, and FIG. 21 is a graph that quantitatively shows the SIR and TPC Command Error Rate when the F-DPCH is received in a normal environment and in a fading environment, where A is the characteristics in a normal environment, and B is the characteristics in a fading environment. Using the table shown in FIG. 20, in a normal environment, it is possible to properly convert the Target TPC Command Error Rate to a target SIR, however in a fading environment, it is not possible to perform conversion correctly. For example, when the Target TPC Command Error Rate is 10−2, the target SIR in a normal environment is 0.7 dB, however, in a fading environment, the target SIR becomes 5 dB. Therefore, in a fading environment, the target SIR that should be set to 5 dB is set as 0.7 dB, and as a result, the base station is not able to perform proper power control of the F-DCPH, so a problem occurs in that the transmission to the mobile station is performed at a power greater than is necessary, radio communication resources are used to excess, and the due to this the throughput of the system drops. Moreover, in some cases, the F-DPCH may be transmitted at a power below the reception capability of the mobile station, and in such a case, a problem occurs in that the TPC Command Error Rate cannot be obtained as a target.
A technique has been disclosed as prior art in which reception quality is measured with good precision (see WO 2007/004292). In this prior art, reception quality that is calculated in the past is saved as a first reception quality, and the current reception quality is calculated as a second reception quality, the difference between the second reception quality and first reception quality is then calculated as a correction value, and the reception quality is corrected using this correction value.
However, this prior art is not a method for accurately measuring the RSCP (Received Signal Code Power) and ISCP (Interference on Signal Code Power) in the F-DPCH channel, or calculating the SIR correctly. Moreover, the prior art does not disclose a technique for accurately measuring the RSCP or ISCP in the F-DPCH channel. Furthermore, this prior art is not a method for performing transmission power control so that the desired error rate is obtained.